the result of the coronavirus has significantly altered the understanding of how early the virus may have been circulating in this country. Researchers now believe that hidden outbreaks were creeping through cities like Chicago, New York, Seattle and Boston in January and February, earlier than previously known.
The new timeline has lent credence to a question on the minds of many Americans: Did I already have the coronavirus?
The retroactive search is happening on many levels. People who had suffered dreadful bouts with flulike illnesses are now wondering whether it had been the coronavirus. Doctors are thinking back to unexplained cases. Medical examiners are poring over their records looking for possible misdiagnosed deaths. And local politicians are demanding investigations.
Brian Gustafson, a coroner in Rock Island County, Ill., said he had no capability to perform post-mortem coronavirus tests, but firmly believed that coronavirus deaths and illnesses were missed across the country during weeks, early this year, when the authorities believed the virus was mainly overseas.
Included in Mr. Gustafson’s suspicions of an undercount: himself. He is convinced that he had the coronavirus in January, when he was so crushingly tired and feverish, he could scarcely summon the strength to walk to the bathroom from his bed.
“I think it was here long before we knew it,” said Mr. Gustafson, who is also a nurse and said he believes that he contracted the virus from one of the recently deceased people who was brought to the coroner’s office long before anyone in Illinois was looking for positive coronavirus cases. “That’s the only logical thing I can think of.”
Some people have spent part of their days sheltering at home going over the details of their bouts with what could have been the coronavirus. In Rothschild, Wis., Tommie Swenson and his girlfriend, Tammy Swikert, keep thinking of the illness they contracted during the winter that spread widely through their village of 5,000 people.
It was nothing like the flu, said Mr. Swenson, a retired truck driver. Milk and soda tasted funny, or like nothing at all. He could barely sleep at night, he had such a rattling cough and felt a crushing weight on his chest.
“We talk about it all the time,” Mr. Swenson said. “What if we did have the coronavirus? Are we immune to it now, or are we going to catch it again? What does this mean?”
Infectious disease experts say the answer is complicated. Many believe that between five and 20 times more people have been exposed to the coronavirus than have tested positive, and there is a growing body of data to support that.
But the likelihood that you are one of them varies based on where you live. Blood tests that can detect coronavirus antibodies may have high false positive rates when exposure to the virus in a given population is relatively low. It was also a bad year for seasonal influenza, so if you felt lousy in January or February, there is a decent chance you had the flu. And even as more reliable antibody tests become available, it is not known how long people who have antibodies may be immune to the virus.
“Everyone desperately wants to be immune to this thing,” said Andrew Noymer, an associate professor of public health at the University of California, Irvine, “and they’re projecting their hope onto the data.”
Beyond the yearning to know one’s own status, knowing how many people in a population have been infected is important because of herd immunity. Since an infected person is thought to pass the virus on to two or three other people, for the virus to stop spreading, at least 50 percent of the population has to have been exposed.
“In terms of policy decisions, we’re nowhere near herd immunity, so that’s the answer,” said Natalie Dean, an assistant professor of biostatistics at the University of Florida.
In hard-hit New York City, about 21 percent of supermarket customers who were tested for coronavirus antibodies tested positive, Gov. Andrew M. Cuomo said on Thursday. If that rate proved consistent across the city, that would mean that about 1.7 million people — or 12 times the number of now confirmed cases — have had it.
But in California, experts say, the number of infected people is most likely below 5 percent — and as in other places where the cases and deaths per capita is lower, the size of the infected population is harder to gauge with currently available rapid antibody tests.
Experts said it would take time to develop, validate and deploy antibody tests that are reliable, and to understand their significance when it comes to individual immunity.
“Yes, people will in this country be able to find out, but not today,” said Eva Harris, a professor of infectious diseases at the University of California, Berkeley, who is studying exposure to the virus over time in the Bay Area.
Deaths from January and February are also getting new scrutiny after an announcement this week in Santa Clara County, Calif., that a woman who died on Feb. 6 had been found to have the coronavirus. Her death occurred weeks earlier than what had previously been thought to be the first death in the United States from the virus.
Dr. Michelle Jorden, the Santa Clara County Medical Examiner-Coroner, said her office was investigating other deaths as well. Her office has sent samples of suspicious cases to the Centers for Disease Control and Prevention, and some are still pending.
Gov. Gavin Newsom of California has said investigators were looking at coroner and autopsy reports going back to December in some of the state’s counties to determine if there might be other, earlier deaths caused by the coronavirus.
Experts said it would be difficult to distinguish, in hindsight, between the seasonal flu and the coronavirus.
Dr. Jeffrey V. Smith, the Santa Clara county executive and a medical doctor, said his wife, also a doctor, reported being puzzled by patients she was seeing in the Bay Area in December.
“I remember her telling me back in December of a number of patients who came in with flulike symptoms who were testing negative for the flu,” Dr. Smith said. “I just wonder if those were patients that had coronavirus.”
In February, experts said, tests were scarce and C.D.C. guidelines for administering them were stringent, leaving all sorts of unanswered questions now.
“There was this weird, uncomfortable silent period,” said Dr. Sara Cody, the chief health officer of Santa Clara County. “We were hearing about all these people who were ill, but they didn’t meet the test criteria so we weren’t testing them.”
Dave Cortese, a member of the board of supervisors of Santa Clara County, requested a full list of deaths in the county from January to March, a period in which he says the county experienced more deaths than the year earlier.
“I am calling for the county to redouble its efforts to release information about all deaths from Covid-19,” Mr. Cortese said, “and tie data points together to provide a completely candid analysis of the information we have.”
For those whose family members have been sickened, the gnawing question — was it Covid-19? — lingers.
The family of Ian Carrier, 36, has struggled to understand the underlying illness that sent Mr. Carrier to a hospital in San Francisco on Christmas Day with a fever and a severe cough. He spent two months there, and was intubated and put on a ventilator, before being released.
April Slone, Mr. Carrier’s sister, said that he had long grappled with significant health issues, but that doctors could not explain his condition. He tested negative for the flu.
“Every day it was something new,” said Ms. Slone. “We couldn’t figure it out.”
Then Ms. Slone read about a link between the coronavirus and kidney problems, an issue Mr. Carrier had begun experiencing.
“That’s when the light bulb went on,” Ms. Slone said. “I called my parents and said, ‘I think he had Covid’ and they said, ‘We do, too.’”
This week, Mr. Carrier returned to U.C.S.F. Parnassus hospital for complications resulting from the kidney problems, his family said. They have been seeking antibody testing for Mr. Carrier, hoping that doctors will learn whether he was exposed to the virus in December, though it is uncertain whether a test will be available
Kristen Bole, a spokeswoman for the hospital, declined to comment on Mr. Carrier’s case but said antibody tests were primarily being used as a tool to improve the diagnosis of patients with current symptoms and for people planning to donate plasma or take part in vaccine trials.
In Oakland, Calif., Kevin F. Adler said he wonders now about his grandfather, Jason Adler, 97, who died on Feb. 2. A nursing home director described his death as tied to “respiratory issues,” the younger Mr. Adler said.
In the days after his death, Mr. Adler said, another person in the small nursing home died, and Mr. Adler’s family members grew ill with sore throats and fevers. That has left the family wondering.
“It’s important to understand how something like the coronavirus was potentially affecting our communities, and especially vulnerable groups, way before there was a national understanding of what was going on,” Mr. Adler said. “In my family’s case, it was just one person. But there are likely hundreds of families like us.”
Julie Bosman reported from Chicago, Thomas Fuller from San Francisco, and Amy Harmon from New York.
